The invention relates generally to semiconductor fabrication and processing equipment and, more particularly, to an improved manual wafer lift.
Semiconductor wafers are typically stored, processed and/or transported in cassettes that have a series of parallel slots, each of which receives and holds a single wafer. The cassettes are also commonly referred to as wafer xe2x80x9cboatsxe2x80x9d, particularly for those used in wet processing operations. Most wafer cassettes hold up to twenty five wafers. The gap between adjacent wafers varies between about xe2x85x9xe2x80x3 for six inch diameter wafers to about xc2xcxe2x80x3 for eight inch diameter wafers. During the manufacturing process, individual wafers are inscribed or imprinted with identifying information, such as lot numbers and processing and test information. This information, which is typically located along the perimeter of the wafer, must be read periodically by technicians, operators or processing machines. However, because of the close spacing of the wafers in a cassette, it is difficult to read the information without removing the wafers from the cassette or otherwise exposing the perimeter of the wafers. Manually lifting the individual wafers is time consuming and expensive and increases the risk of contaminating the wafers.
Conventional wafer lifts, such as the H-Square Corp. xe2x80x9cWafer Escalatorxe2x80x9d, utilize a passive mechanism wherein a stationary angled contact surface engages and lifts the wafers as the cassette is lowered onto the escalator. The present invention provides an alternative to such passive devices by using an active lifting mechanism that allows the operator to raise the wafers after the cassette has been placed on the machine. Thus, the operator is able to better control the extent to which the individual wafers are raised and lowered.
The present invention provides a new lift for lifting a series of vertically oriented wafers arranged parallel to one another in a cassette. Broadly stated, the wafer lift comprises a lift plate and an actuator mechanism for raising the lift plate. The lift plate has a contact surface for engaging the edge of each of the wafers. The contact surface extends upward at a predetermined angle so that, when the lift plate is raised and the contact surface engages the edges of the wafers, each wafer is lifted incrementally higher than the preceding wafer. In one aspect of the invention, the actuator mechanism includes a bell crank rotatable about a pivotal axis for transforming rotational motion into translational motion. The bell crank has first and second crank arms that extend radially from the pivotal axis and an arcuate member that extends circumferentially between and joining the crank arms. Thus, the arcuate member forms the circumferential perimeter of the bell crank. The actuator mechanism also includes a transmission mechanism for transmitting the translational motion of the perimeter of the bell crank to the lift plate to raise the lift plate so that the contact surface engages the edges of the wafers.
In another aspect of the invention, the transmission mechanism consists of a lift belt linking the bell crank and the lift plates. One end of the lift belt is attached to the perimeter of the bell crank and the other end is operatively connected to the lift plate for vertical movement therewith. The lift belt runs under a first roller and over a second roller. The belt has a first segment between the bell crank and the first roller, a second segment between the first and second rollers, and a third segment between the second roller and the lift plate. The rollers are configured so that rotation of the bell crank about its pivotal axis pulls the first segment of the belt upward, the second segment downward and the third segment upward to raise the lift plate to engage and lift the wafers.
In one preferred version of the invention, the wafer lift is actuated by pulling down on a lever type handle attached to the bell crank to rotate the bell crank and thereby raise the lift plate to engage and lift the wafers. When the handle is lowered, the bell crank returns to its rest position under the weight of the lift plate and the wafers.
Another version of the invention utilizes a pair of upright lift plates that are positioned parallel to one another above the bell crank. Each lift plate is rigidly connected to the other and slidably mounted on a plurality of vertical shafts, for coordinated reciprocal vertical movement thereon. One end of the lift belt is attached to the perimeter of the bell crank and the other end is attached to a connector that rigidly connects the lift plates. The lift belt runs under the first roller, which is located below the horizontal plane intersecting the pivotal axis of the bell crank, and over the second roller, which is located above the connector. The belt has a substantially vertical first segment between the bell crank and the first roller, a substantially vertical second segment between the first and second rollers, and a substantially vertical third segment between the second roller and the lift plate. Thus, upon rotation of the bell crank about its pivotal axis, the first segment of the belt is pulled upward, the second segment is pulled downward and the third segment is pulled upward to raise the lift plates to engage and lift the wafers.